For many applications it is important to control the amount of material that is present in a flow of a flowable substance. For other applications it is important to control the distribution of material added with a flow of a flowable substance. For still other applications it is important to control both the amount of material that is added with a flow of a flowable substance and the distribution of material added with the flow of a flowable substance. To control the amount of material added and/or to control the distribution of material added, it is important to measure or monitor the volume flow of a flowable substance.
For steel fibre reinforced concrete it is extremely important to control the amount of reinforcing fibres added to the concrete and/or to control the distribution of the reinforcing fibres over the concrete volume. Control of the amount and/or the distribution of steel reinforcing fibres added to the concrete is for example important to guarantee a correct reinforcement. Especially for structural applications strict process control and/or quality control is important.
At present it is difficult to control the amount of fibres added to fibre reinforced concrete once the reinforcing fibres are in the concrete, fresh or hardened. Today process and quality control is done by wash-out tests. In wash-out tests at regular intervals during the unloading of the concrete samples of concrete are taken from the truck mixer. As wash-out tests require sampling, weighing, washing out and counting or weighing of the steel fibres, these tests are time consuming and labour intensive. Furthermore these tests have the disadvantage that they require special equipment and might deliver results too late.
There are instruments available on the market to determine the amount of steel fibre present in a cube of concrete (fresh or hardened) by inductive measurements. A drawback of this technology is the required calibration. Furthermore this technology does not allow on-line measurement. The samples need to be filled completely with concrete and three measurements are required along the three main axes to determine the amount of steel fibres present.
Therefore it is clear that there is an urgent need for control mechanisms to measure or monitor the amount and/or distribution of steel reinforcing fibres during the unloading of the steel fibre reinforced concrete.